1. Field of the Invention
The invention relates generally to the field of aircraft access to floating structures. More particularly, the invention relates to helicopter landing pads or platforms associated with floating structures such as seismic survey vessels.
2. Background Art
Floating marine structures known in the art include marine seismic survey vessels. Such vessels are used to tow seismic survey sensors and seismic energy sources in a body of water such as the lake or the ocean. Seismic survey seismic vessels typically include onboard equipment, known collectively as a recording system, that makes records with respect to time of signals generated by the seismic survey sensors, determines geodetic position of the seismic vessel, energy source and sensors at any time, and actuates the source at selected times.
As with any marine seismic vessel, at least some personnel are required to navigate the seismic vessel, and operate the various seismic data acquisition equipment on board the seismic vessel. Typically, seismic survey seismic vessels include a helicopter landing pad to facilitate movement of personnel onto and from the seismic vessel while the vessel is at sea. As a matter of personnel safety, however, there are limits to the amount of seismic vessel movement, other than in the direction of travel of the seismic vessel, for which helicopter landing and takeoff can be safely performed. Such movement has three components known as pitch, roll and heave. Pitch is rotation of the seismic vessel about a horizontal axis transverse to the centerline of the ship. Roll is rotation of the seismic vessel about its centerline. Heave is motion of the ship upwardly and downwardly. Regulatory authorities in some countries, for example, have imposed limits of two degrees maximum pitch and roll for which helicopter landing is permitted. Heave of more than one or two meters may also make it unsafe to land a helicopter on a seismic survey seismic vessel.
U.S. Pat. No. U.S Pat. No. 1,558,567 issued to Schein discloses a system for compensating pitch and/or roll motion of an aircraft landing platform on a floating vessel. U.S. patent application Ser. No. 11/345,013, now U.S Pat. No. 7,152,547, assigned to the assignee of the present invention, discloses a system for compensating an aircraft landing platform on a floating vessel for pitch, roll and heave.